1. Field of the Invention
The present invention relates to a developing apparatus, a developing method, an image forming apparatus and an image forming method utilizing an electrophotographic method.
2. Description of the Related Art
A large number of electrophotographic methods are known, and in general, a photoconductive substance is utilized and various units are used to form an electrostatic latent image on an electrostatic latent image bearing member. Then, the electrostatic latent image is developed by a toner to be formed into a visible image, a toner image is, if necessary, transferred to a recording medium such as paper, and the toner image is then fixed on the recording medium by heat or pressure to provide a copy. Such an image forming apparatus includes a copier and a printer.
Such printer and copier have been converted from an analog type to a digital type in recent years, and have been strongly demanded to be excellent in reproducibility of a latent image and to have a high resolution, and, at the same time, in particular the printer has been strongly demanded to be reduced in size.
Heretofore, a printer has been often used in such a manner that the printer is connected to network and used by a large number of persons for printing, but, in recent years, a PC and a printer have been increasingly demanded to be placed on a desk for each individual and used for printing thereat. A printer is thus required to be smaller in footprint, and is strongly demanded to be reduced in size.
In addition, even such a compact printer is highly demanded to provide a high-quality image and to be high in durability so as to provide an image small in fluctuation of quality even for a long time of use.
In focusing on a reduction in size of the printer here, it is mainly effective for the reduction in size to reduce a fixing unit and a developing apparatus in size. In particular, the developing apparatus accounts for a significant portion of the printer, and the reduction in size of the developing apparatus can be said to be essential for the reduction in size of the printer.
With respect to a developing system, a developing system for the printer, including a 2-component developing system and a 1-component developing system, is suitably a 1-component developing system which is compact. The reason for this is because a member such as a carrier is not used in the 1-component developing system.
Then, with respect to the reduction in size in the 1-component development, it is effective for the reduction in size of the developing apparatus to reduce the diameter of an electrostatic latent image bearing member or a toner carrying member. In terms of high image quality, a developing system (hereinafter, referred to as “contact developing system”) can be adopted in which the toner carrying member and the electrostatic latent image bearing member are arranged in contact with each other.
The contact developing system in which the diameter of the toner carrying member is lowered, however, puts an increased load on a toner, easily causing the reduction in image quality for a long period of use. The reason for this is because the diameter of the toner carrying member is lowered, thereby, for example, causing the increase in number of passages through a toner supply member arranged in contact with the toner carrying member or the increase in curvature to result in the increase in abutment pressure at an abutment portion.
The toner supply member has been conventionally rotated in the same direction as in the toner carrying member, and the respective movement directions at the abutment portion of the toner supply member and the toner carrying member have been often opposite to each other. The reason for this is because it is easy to scrape a toner not developed and at the same time supply a fresh toner, and thus the increase in image quality is easily achieved.
Such a system in which the toner carrying member and the toner supply member are rotated in the same direction easily provides a high image quality, but has the following problem: the toner carrying member and the toner supply member are moved in the opposite direction to each other at the abutment portion therebetween to easily cause toner deterioration for a long period of use.
On the contrary, for the purpose of decreasing the load on a toner to maintain a high durability, a system has been started to be adopted in recent years in which the toner carrying member and the toner supply member are rotated in the opposite direction to each other to decrease the fluctuation in image quality even for a long time of use. Alternatively, an attempt has also been proposed in which no toner supply member is used to thereby maintain a higher durability (see Japanese Patent Application Laid-Open No. 2005-173484 and Japanese Patent Application Laid-Open No. 2006-154093).
In such a developing apparatus, however, the particular problem tends to be easily exposed. One is the problem called “regulation failure”. The regulation failure refers to a phenomenon in which a difference is made between the amount of a toner on the toner carrying member immediately after the consumption of a toner (hereinafter, referred to as “after black imaging”) and the amount of a toner on the toner carrying member in the state of no consumption of a toner in a non-printing region or the like (hereinafter, referred to as “after white”), specifically, refers to a state where the amount of a toner on the toner carrying member after white is larger.
If such a regulation failure is caused, for example, an image defect called “ghost”, namely, an image defect including spot-like and wave-like variations on a non-printing area, and a toner lump on an image is caused.
With respect to the regulation failure here, the regulation failure is caused by pasting a toner on the toner carrying member onto the toner carrying member by a mirroring force or the like, and in particular is easily caused under a low-temperature and low-humidity environment.
For the reduction in attachment force, an attempt has been proposed in which a silica having particular water content and volume resistivity, produced by a sol-gel method, is used to reduce the physical attachment force of a toner (see Japanese Patent Application Laid-Open No. 2002-108001).
In addition, a toner has also been proposed which is good in fluidity and excellent in charge stability by combination use of a silica produced by a sol-gel method and a silica produced by a dry method (see Japanese Patent Application Laid-Open No. 2012-189876).
Such techniques, however, are insufficient particularly in terms of the effect in the case of a long period of use in a low-printing rate, and have a room for improvement.
On the other hand, the reduction in amount of a toner charged and the reduction in mirroring force solve the regulation failure, but fogging in a no image region is severer under a high-temperature and high-humidity environment, and there is a room for improvement in suppressing the regulation failure under a low-temperature and low-humidity environment and the fogging under a high-temperature and high-humidity environment at the same time.